Generally, important matters required for enhancing pipetting precision are to detect a level of a blood serum sample and a reagent or similar liquid, to measure a pipetting rate thereof, to measure an absolute sucking rate thereof, to adhere the liquid to the outside of the nozzle, and to detect contamination thereof by foreign matters such as bubbles and fibrins.
For this reason, conventionally, a method has been employed, in which an electrode is immersed in the liquid together with the nozzle and the liquid level is detected according to a conductive state with the electrode so that an inserting rate (distance) of the nozzle to the liquid is controlled, but in the case of this method, the electrode must be immersed into the liquid, so that the electrode must be washed after each measurement thereof to prevent cross contamination, and as a result, there have been such problems as that a device becomes complicated, and that size and cost of the device increase.
Then, recently a method of detecting a liquid level using a pressure sensor was proposed. In this method, a sucking pressure of the nozzle when a vapor is sucked is different from that when a liquid is sucked, so that the liquid level is detected by detecting the difference between the pressures, whereby an inserting rate (distance) of the nozzle to the liquid is controlled, and for this reason only the nozzle is contacted with the liquid, and the method has such advantages as that a cleaning function is not required, which makes it possible to simplify the device as well as to reduce the costs.
However, the method of detecting a liquid level using a pressure sensor has several problems such as that the resolution is low and the sensitivity is not high, and also that the method is easily affected by an atmospheric pressure as well as by pressure change due to the sucked air, and also affected by vibrations generated due to upward/downward movement of the nozzle as well as by a noise of the pipetting device itself or a change of a voltage, and for this reason malfunction thereof occurs quite often, and the reliability thereof as a measuring means is quite low.
An optical liquid level detecting means is far more effective as a means to solve the problems as described above, and various means in which both an optical fiber for irradiating a light therethrough and an optical fiber for receiving a light are provided outside the nozzle for receiving a reflected light from a liquid level with the optical fiber for receiving a light to detect the level thereby are proposed for the liquid level detecting methods based on the conventional technology.
However, in the liquid level detecting means using a light for detecting a liquid level based on the conventional technology, in which both a fiber for irradiating a light therethrough and an optical fiber for receiving a light are provided outside the nozzle for catching a reflected light from a liquid level with the optical fiber for receiving a light to detect the level thereby, these fibers have to be inserted in parallel to each other together with the nozzle into a vessel for a liquid, and for this reason it can not be denied that the method has a possibility of cross contamination caused by the fiber contacting with the liquid adhered to the wall surface of the vessel for a liquid, and also the amount of light caught by the optical fiber for receiving a light is extremely small, which makes it difficult to accurately detect a liquid level, and in addition the extremely minute control is required, which is difficult because there also occur some cases where a timing for receiving the reflected light is shifted or a light can not be received by the fact that the liquid level becomes slightly wavy due to vibrations of the device.
The present invention was made to solve the problems as described above, and it is an object of the present invention to provide an entirely new method of sucking/determining a liquid, including, for instance, detection of a liquid level in which a light receiving body is provided in a nozzle, and fluctuation of a light in a disposable tip such as a pipetting tip or in an opening section at the lower end of a tip of a cleaning system are detected thereby from the side of nozzle under circumstances similar to seeing the other opening section from one end of a tunnel, so that it is possible to extremely sensitively detect a liquid level, contamination by foreign matters therein, or an interface between liquids each having a different color without being affected by the wavy liquid level, as well as to provide a pipetting device driven and controlled according to the method. Namely, a basic principle of the present invention is characterized in that the various types of detecting operation are carried out by catching a moment as if a light instantly changed shows fluctuation in a flash when a near-by substance in a space cut off from the outside of the environment is changed, for instance, from vapor to liquid.